I have been skiing on a friends lake nearby that is only 320m by 50m with a 2/3 course and it is really quite tight but adequate. I don't have length constraints, maybe I can look at this a little more. Now is the time to change it! I have an extremely wet property and plan on filling it from a sump alongside with drains feeding it. I can then pump it over the bank. Because my rainfall is not guaranteed I was intending on my calculations, of having the banks 3m high by 3m wide at the top. This should give me approx. 3.5 metres after needing .5m soil removed from floor. Ie. Planning on 3.3m(11') water. I hear you all say gooooo longer. I actually have a natural lake that I deepened to 4.5m not far away and it is holding well, I have this stocked with fish. So I have had a small trial run. It's only about 2Ha (5acres) and round,due to native vegetation I couldn't make it any bigger. I wasn't intending on putting in turning islands and a slope of something like 1 in 2.5/3 on the inside bank, is this enough slope?

I have been skiing on a friends lake nearby that is only 320m by 50m with a 2/3 course and it is really quite tight but adequate. I don't have length constraints, maybe I can look at this a little more. Now is the time to change it! I have an extremely wet property and plan on filling it from a sump alongside with drains feeding it. I can then pump it over the bank. Because my rainfall is not guaranteed I was intending on my calculations, of having the banks 3m high by 3m wide at the top. This should give me approx. 3.5 metres after needing .5m soil removed from floor. Ie. Planning on 3.3m(11') water. I hear you all say gooooo longer. I actually have a natural lake that I deepened to 4.5m not far away and it is holding well, I have this stocked with fish. So I have had a small trial run. It's only about 2Ha (5acres) and round,due to native vegetation I couldn't make it any bigger. I wasn't intending on putting in turning islands and a slope of something like 1 in 2.5/3 on the inside bank, is this enough slope?

If you don't have length constraints, go 2,400'. Put in a full course complete with 55m buoys. It's more work and requires more water to fill, but anything worth doing is worth overdoing. But even so, I would narrow the lake a bit. 175'--225' is plenty wide. Making it narrower helps with preventing the wind from making the rollers ridiculous.

Also, you want a graded slope up to the banks so that the boat wakes can dissipate easily. Start off with a 10:1 slope at the shoreline. After a bit of distance, you can increase the slope to 3:1 so it is not too shallow where people are skiing.

Also, before you start, consider where the prevailing winds are and how that will affect things. After that, consider where the sun will be in relation to the course at dawn and sunset. If you orient it east/west, during early and later hours, it may be unskiable going in one direction.

There's lots of info out there on the interwebs on building ski lakes. Give it a good read and plan carefully so, in the end, you don't wish you had done something differently.